When mysqlbinlog reads binlogs from a remote server (with stop-never), it connects to the server with a certain ID, either default or explicitly set. If another instance of mysqlbinlog connects with the same ID, the previous one exits. In MySQL, it returns a non-zero exit code and a clear enough error message:

ERROR: Got error reading packet from server: A slave with the same server_uuid/server_id as this slave has connected to the master; the first event 'mysql-bin.000001' at 4, the last event read from './mysql-bin.000051' at 4700, the last byte read from './mysql-bin.000051' at 4700.

In MariaDB, it exits silently with success code and without error messages. It's dangerous, because it will make user believe all logs have been stored.